Method for the production of an improved metal/ceramic material and articles



United States Patent 4 Claims. drab-191.12

The invention relates to a processfor, the production of an improved metal/ceramicmaterial and articles made therefrom, and relates especially to ceramic materials and shaped articles which contain a metalskeleton.

It has been known for some time that metal fibres, which: are usually obtained by cutting frommetal wires, filamentsand thelike, can be fel-tedtogether and, as

felts, canbe sintered. to shaped articles (so-called fibre metallurgy). It is also known thataporous skeletonlike metal molded article so'producedis ableto-serve as a reinforcing structure for, for; example, pure magnesium.

Following'on' from this it was hoped that it would be possible to build the metal fibres into; ceramic composition-s as reinforcement. Experiments showed, however, thatwhen the usual iron orsteel' wool was used. together-with a fluid suspension of ceramic powders in liquids (so-called slip)-, such asthose with aluminum oxide as the main constituent no metal/ceramicarticles with useful properties could be obtained. Thisisprobably caused in part by the formation of iron-aluminum oxide spinels, which have'very badmechanicalproperties and, in comparison with aluminum oxide, a very low eutecticmelting point of 1310 C.

It has now been foundthat these disadvantages can beremoved and a metal/ceramic material with goodmechanical, thermaland chemical properties can beproduced-by first subjecting metal wool, especially-steel:

wool; to a diffusion treatment with a relatively inert metal thereby improving the heatand corrosion-resisting qualities, then annealing and; after cooling, treating with suitable ceramic, oxide/ceramic ormetal/ceramic slips, drying and ifdesired compressing the drying mass while being in a. leather-hard condition.

Itis also possible to stratify the steel wool, beforethediffusion treatment, in the form. of single fibres, and to press. it'to any desired shape. After this the diffusiontreatment is effected.

It has been found expedient to use the steel wool in fibre thicknesses ofa-maxir'nurn of- 0.6 mm., preferably less than 0.1 mm. As a. general principle the thickness of the fibres should be the smallest. possible, i.e the lower. limits for the thickness of the fibres are set by the process of preparation for the steel wool. It has further been foundi'that the carbon content of the steel may be varied within relatively-wide limits. In theprocess according to the invention a steel wool with more than 0.1% of carbon may be used; in some cases even with. more than 1% of carbon. The steel wool, the

difiusi-on metal, the diffusion. process, andv the oxide/ ceramic mixture must be chosen with respect to composition so that everything is successively synchronised. These are the usual tasks for the technicians in the metal and ceramic fields.

For some uses it may be expedient to provide the surface of the shaped article produced, after drying, with an additional coating of a carbide ceramic slip, preferably by dipping or spraying. The metal/ceramic so obtained consists according to the invention of a metallic and a ceramic phase, which are interconnected together at the phase boundaries in the form of interlocking net- Patented Feb. 8, 1-966 works, while the metallic phase may consist of homogeneously, chromed steel wool. The ceramic phase, just as. the steel wool skeleton, is a network and only the subsequentlyv applied surface layer. is a continuouslayer. This material according to the invention possesses excellentv mechanical, technological, thermal, oxidation-resisting and corrosion-resisting properties, which is to be attributed to the fact that the homogeneously chromised steelwool possesses-a good adhesion to ceramic compositions, especially to aluminum oxide.

The good adhesion. between chromisedsteel wool andceramic according to the invention mayv possibly be ate tributedto a mechanism similar to that known from com-. biuation-materials using aluminumoxide and chromium powder, which. materials show a transition. phase of.

chromium. oxide-a1uminum oxidespinel (ruby): formed at the Phase boundaries between. the chromium metal and, aluminum, oxide.

The relative amounts of ceramic material (aluminum oxide) and chromised steel woolto beuseddependupon.

the, purposeof user, The, greater the properties of chromised steel wool,- the. higher is the toughness and.

impact strength of the finishedgmaterial. Asa rule parts by volume, of; aluminum, oxide and; chromised steel wool 1 n t e, propor ion f- 1 :1: reaim s In; as ditiomthe density of the material according to the invention cambe-adjusted to the intended :Purpose and,

vary with-the' preparation Whenthe metalfibres, which mayabe cutt-o certain suitable length, e.g. to 5-50 mm., are chromised and annealed and the resultant fibres,

now homogeneouslyaenriched with,chromium, are mixed with the slipand then sintered in a, furnace, a compar a.

tively dense material with a bulk density between 4.0 g./cc. and 5.0 g./cc. results. Higher bulk densities are obtained when this material is compressed as, after'the he; P nd ag in are mp es ed wh n. ei the leather-hardst-ate, after 'hayingbeen dried. Th-isprocess. isespecially suitable. for theproduction of parts,of CQIH'.

plex shape, especially turbine blades.

If; steel 1 wool with a: relatively high carbon content is sed; euon r mi n y a e moun s ph m r urn carbide are; formed in the chromiurn alloy. Since carbides; have a more or less.cerarnic like,character,the bindingofsuch a steel wool in the ceramic b ase material. Eor this reason according to the present.

is; Still better. inventionthe chromising of steel wool with a higher carbon content is preferred, which is in contrast to the recommendations in the literature, according to which;

the carbon content in every case is said-to be not allowed. toexceed 0.1%,;

Suchamaterial may beconverted-into ceramic cutting discs with relatively. goodcu-tting properties by coating with; a, so-called cermet-material, which possesses especially good cutting properties. The said cermet-mate-rial means a powder combination of ceramics and re fractory metal oxides. with other metals and alloys, especially such as aluminum oxide-chromium combinations, and is described by Blackburn, A. R. and Shevlin, T. S. in,P.rogress Report on Fabrication and Physical Properties of Chromium-Aluminum Oxide Cermets, Ohio State University, April 1949 (Report N. 53). The coating of cermet-material is applied to the dry steel wool/ceramic body by dipping or spraying and postsintering the whole. Upon use as a cutting tool, the steel wool/ceramic body part plays the role of providing the strength, whereas the coating part provides the cutting properties.

Athin coating layer of a'few tenths of a millimetre of the cermet issufficient-r These'=cutting discs cannot *of course be subsequently sharpened, but must be used as expendable discs.

Theshaped articles produced by the process according to the present invention, on account of their'g're'at strength and good heat conductivity, are particularly advantageous for use as material for machine parts and cutting discs. The following examples are for the purpose of illustration, only, without limiting the present invention in scope.

' Example] a Steel wool-v in the form of many single fibres witha fibre thickness less than 0.01 mm. and" an average fibre width of about 0.1 mm. was prepared by chipping off from a special steel .wire with the following analysis: 0.13%, C, 1.06% Mn, 0.042% P, 0.009% S, 0.05% CI and traces of Si. The length of the fibres was variable and extended up to a few metres. The steel' wool so obtained was packedtloosely in a suitable: chromising vessel with-pieces of chromium and. subjected to a chromium diflusi'on treatment with gaseous hydrogen chloride for 3 hours at 1100 C. The steel wool was then annealed at 1300'? (ES-for 5 hours under a reducing atmosphere, whereby a ho-" mogeneous distribution'of the chromium "over the whole fibrous cross-section of the steel wool is Obtained.

After cooling, a steel wool resulted which had an average chromium content of about 30%. tained was again split up into separate fibres and mixed with a composition consisting of 95% A1 and of kaolin. This mixture was compressed in a mould at a pressure of 5 tons per cm. and sintered in vacuo. at After cooling, a shaped-bo'dy 1550 C. for 1 hour. was obtained which consisted of ceramic and 50% by volume of chromised steel wool and which had a: good heat conductivity as wellas-compar atively high strength. 1

.Example 2 The metal wool was prepared from steel wire-as described in Example 1', and the fibres arran'ged in.a-"wdi rected form in separate layers and at various angles to' The-fibresso arranged were first com'-- pressed in'a rectangular mouldwith a pressures'of 0.5

one another.

ton/cm A mutual interlocking of the separate fibres took place, so that after the pressing the pressed "body already had a shape corresponding somewhat to the final form. I

The preliminary moulded body was now chromised by the process described in Example 1. The chromising temperature however was 1200 C. and the chromising time 2 hours. After this period, the current of hydrogen chloride was stopped and the chromising vessel purged with hydrogen, the temperature being maintained for a Example 3 A shaped body was first moulded from steel wool as in The steel wool so 0b.:

. l Example 2 and subjected to sintering for 1 hour at 1350 'C.-in-a' current ofhyd-rogen. The--indi-vidual-fibres are welded together by this treatment, and the steel wool skeleton possesses a high strength with very great porosity. The steel wool framework was then chromised for 3 hours at 1100 C., as described in Examples 1 and 2, A subsequent equalising annealing at 1300 C. in a current of hydrogen brought about hon'iogenisation'of the content "'1 of chromium. The annealing period was about 5 hours.

The skelet-albody so obtained'was saturated in vacuo with a ceramic slip-according to Example 1, dried in air at 95" C: and'then compressed at 2 tons/cm. 'while in the-leather-hard"condition. The final sinte-ring tookplace 'at 1550 C. for 1 hour in a high vacuum. Thmetal-ceramic body so obtained had very good properties.

Example'4 Ashaped body was .preparedbythe process given in Example 2 and chromised, but the carbon content of the steel Wool amounted to 1.2%,

and 2 and dried. It was then dipped into a fluid carbide/ ceramic slip composition and the excess carbide/ceramic suspension was removed by draining off, so that only a layer of about 0.2 mm. thickness remained adher ing thereto. This shaped body obtained further plastic properties through the suspension liquid adsorbed and was then dried while in the leather-hard state and compressed with 6 tons/cm. in a steel mould. The sintering was effected in vacuoat 1700: C. fora periodof l hour. The shaped body sofobtained, after careful grind ing with'a diamond hetstone, could be used for ma-- itchining on a lathe.

We claim:

1.- A method of producing a-body of metal fibers in a ceramic matrix, comprising contacting a body of ferrous metal fibers with metallic chromium and heatingthe body.

" of metal fibers to diffuse the chromium throughout the thickness of the fibers, thereafter impregnating thebody of jfibers with a ceramic slip,- and thereafter sinteringthe ceramic. of the impregnated body.-

2. A method as'claimed in claim l, in which the ceramic- 5 is principally aluminum oxide.

.,1;A method as claimed in claim rous metal has a carbon content in excess-.o-f 0.1%

4. A metal fiber ceramic impregnated material compris ing a metallic phase inrthe form of an interlocking network-of homogeneously chromised steel wool of a thickness upto about 0.6 mm.,,the network being impregnatedwith afused ceramic material which adheres firmly to the steel wool. r

I References Cited by the Examiner UNITED STATES PATENTS 3,068,556 12/1962 Kramer 29-420 X 3,153,279 10/1964 Chessin. 29'419'X I FOREIGN PATENTS -2 10,9 27 10 1957 Australia. I OTHER REFERENCES Fiber Metals, Materials and Methods, Metcalfe et al.,

i November-.1955, pp. 96-98.

WHITMORE WILTZ, Primary Examiner.-

This shaped body as. saturated with the composition mentioned in Examples 1- 1, in which the fervi 

4. A METAL FIBER CERAMIC IMPREGNATED MATERIAL COMPRISING A METALLIC PHASE IN THE FORM OF AN INTERLOCKING NETWORK OF HOMOGENEOUSLY CHROMISED STEEL WOOL OF A THICKNESS UP TO ABOUT 0.6 MM., THE NETWORK BEING IMPREGNATED WITH A FUSED CERAMIC MATERIAL WHICH ADHERES FIRMLY TO THE STEEL WOOL. 